WDPN31 PGTW 251500
MSGID/GENADMIN/JOINT TYPHOON WRNCEN PEARL HARBOR HI//
SUBJ/PROGNOSTIC REASONING FOR TYPHOON 06W (CHAMPI) WARNING NR 019//
RMKS/
1. FOR METEOROLOGISTS.
2. 6 HOUR SUMMARY AND ANALYSIS.

SUMMARY:
   INITIAL POSITION: 23.0N 139.5E
   INITIAL INTENSITY: 65 KTS
   GEOGRAPHIC REFERENCE: 146 NM SOUTHWEST OF IWO TO
   MOVEMENT PAST 6 HOURS: NORTH-NORTHEASTWARD AT 08 KTS
   SIGNIFICANT WAVE HEIGHT: 25 FEET

SATELLITE ANALYSIS, INITIAL POSITION AND INTENSITY DISCUSSION:
ANIMATED ENHANCED INFRARED (EIR) SATELLITE IMAGERY INDICATES THE
SYSTEM CONTINUES TO STRUGGLE TO MAINTAIN PERSISTENT, ORGANIZED
CONVECTIVE BANDS. CONVECTIVE ACTIVITY WANED AFTER 0900Z, BUT HAS
BEGUN TO ONCE AGAIN FLARE NEAR THE ASSESSED LOW LEVEL CIRCULATION
CENTER (LLCC). HIGH RESOLUTION MODEL CROSS SECTIONS INDICATE
MID-LEVEL DRY AIR IMPINGING FROM BOTH THE EAST AND WEST, LIKELY
INHIBITING THE CONTINUED CONSOLIDATION OF THE CONVECTIVE CORE. THE
INITIAL POSITION IS PLACED WITH HIGH CONFIDENCE BASED ON AN
EXTRAPOLATION OF A PARTIAL 2510001Z ASCAT-A PASS, WHICH CAPTURED THE 
CORE OF THE CIRCULATION. WITH THE GENERAL NORTHWARD TRACK OVER
THE PAST SIX HOURS, IT APPEARS THAT TY 06W HAS REACHED THE AXIS OF
THE SUBTROPICAL RIDGE (STR). THE INITIAL INTENSITY IS CONSISTENT 
WITH THE MULTI-AGENCY DVORAK INTENSITY ESTIMATES. HOWEVER, CIMSS IS 
CURRENT DOWN, SO THE INTENSITY ESTIMATES ARE BASED ENTIRELY ON 
SUBJECTIVE DVORAK ASSESSMENTS. SEA SURFACE TEMPERATURES (SSTS) 
REMAIN WARM AND VERTICAL WIND SHEAR (VWS) IS LOW WHILE UPPER LEVEL
OUTFLOW IS OVERALL MODERATE. THE EQUATORWARD CHANNEL IS FAIRLY
ROBUST BUT BEGINNING TO BE CONSTRAINED ON TOWARDS THE EAST.
POLEWARD OUTFLOW MEANWHILE IS INCREASING, BUT CONFINED TO VERY
NARROW CHANNEL AHEAD OF AN APPROACHING MAJOR SHORTWAVE TROUGH,
WHICH WILL CONTINUE TO PINCH THE OUTFLOW CHANNEL PROGRESSIVELY
SMALLER OVER THE NEXT 24 HOURS.

INITIAL WIND RADII BASIS: SCATTEROMETER DATA. 

CURRENT STEERING MECHANISM: DEEP LAYER SUBTROPICAL RIDGE (STR) TO
THE EAST. 

AGENCY DVORAK AND AUTOMATED FIXES: 
   PGTW: T4.0 - 65 KTS
   RJTD: T4.0 - 65 KTS
   KNES: T4.5 - 77 KTS

FORECASTER ASSESSMENT OF CURRENT ENVIRONMENT: FAVORABLE
   VWS: 0-5 KTS
   SST: 28-29 CELSIUS
   OUTFLOW: STRONG EQUATORWARD
   OTHER FACTORS: MODERATE BUT NARROW POLEWARD OUTFLOW CHANNEL.

ANALYSIS CONFIDENCE:
   INITIAL POSITION: HIGH
   INITIAL INTENSITY: MEDIUM
   INITIAL WIND RADII: HIGH

3. FORECAST REASONING.

SIGNIFICANT FORECAST CHANGES: THERE ARE NO SIGNIFICANT CHANGES TO
THE FORECAST FROM THE PREVIOUS WARNING.

FORECAST DISCUSSION: TYPHOON CHAMPI HAS REACHED THE AXIS OF THE
STEERING RIDGE, AND WILL BEGIN TO TRACK NORTH-NORTHEAST OVER THE
NEXT 12 HOURS, BEFORE ACCELERATING AND TURNING MORE SHARPLY
NORTHEAST THEREAFTER. THERE REMAINS ONLY A BRIEF PERIOD OF
FAVORABLE ENVIRONMENTAL CONDITIONS, BEFORE CONDITIONS RAPIDLY
DETERIORATE. THROUGH TAU 24, UNDER GOOD POLEWARD AND EQUATORWARD
OUTFLOW, WARM SSTS AND LOW VWS, THE SYSTEM IS EXPECTED TO INTENSIFY
TO A PEAK OF 85 KTS. THEREAFTER THE PASSAGE OF A MAJOR SHORTWAVE
TROUGH OVER THE SYSTEM WILL INTRODUCE WESTERLY CONVERGENT FLOW
ALOFT, WHILE SSTS DECREASE TO LESS THAN 26C AND VWS BEGINS TO
INCREASE, LEADING TO A SLOW WEAKENING TREND THROUGH TAU 36. THE
SYSTEM WILL ALSO BEGIN TO UNDERGO EXTRATROPICAL TRANSITION BY TAU
36 AS IT STARTS TO INTERACT WITH THE BAIU BOUNDARY. AS THE SYSTEM
RACES NORTHEAST TO THE EAST OF TOKYO, SHEAR WILL INCREASE TO OVER
40 KTS, BEGIN MERGING INTO THE BAIU BOUNDARY AND MOVE UNDER THE
200MB JET FLOW, INDUCING EXTRATROPICAL TRANSITION, WHICH IS
EXPECTED TO BE COMPLETED NO LATER THAN TAU 72, AND AS EARLY AS TAU
60. 

MODEL DISCUSSION: NUMERICAL MODEL GUIDANCE IS IN TIGHT ACROSS AND
ALONG-TRACK AGREEMENT THROUGH TAU 36, WITH ONLY A 60NM SPREAD AT
TAU 36. ACROSS-TRACK SPREAD REMAINS VERY LOW THROUGH THE REMAINDER
OF THE FORECAST, BUT ALONG-TRACK UNCERTAINTY INCREASES
SIGNIFICANTLY TOWARDS THE LATER PORTION OF THE FORECAST. THE JTWC
FORECAST TRACK LIKES ALONG THE EASTERN EDGE OF THE GUIDANCE
ENVELOPE THROUGH TAU 24 IN LIGHT OF THE RECENT TRACK MOTION, THEN
LIES CLOSE TO THE MULTI-MODEL CONSENSUS MEAN THROUGH THE REMAINDER
OF THE FORECAST PERIOD. THE JTWC INTENSITY FORECAST LIES ABOVE THE
CONSENSUS MEAN, THOUGH SLIGHTLY LOWER THAN THE PREVIOUS FORECAST,
IN RESPONSE TO THE CONTINUED INABILITY OF THE SYSTEM TO MAINTAIN
DEEP CORE CONVECTION, AND THE LIMITED TIME REMAINING UNDER GOOD
ENVIRONMENTAL CONDITIONS. IF THE SYSTEM CANNOT MAINTAIN THE CURRENT
ROUND OF CONVECTIVE CONSOLIDATION, THE PEAK INTENSITY IS LIKELY TO
BE LOWER THAN THE CURRENT FORECAST.   

FORECAST CONFIDENCE:
   TRACK 0 - 72 HR: HIGH
   INTENSITY 0 - 72 HR: MEDIUM//
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